This article was in The New York Times this morning. It is an interesting read and explains why Microsoft has put off releasing Windows Vista.
http://www.nytimes.com/2006/03/27/technology/27soft.html?ei=5088&en=d0c02cd75d5822fb&ex=1301115600&adxnnl=1&partner=rssnyt&emc=rss&adxnnlx=1143461088-pr16MhX3w8s+O6hS19bgTg